There is one efficient way to broaden an antenna’s frequency range—lower the Q. That is usually done with large-diameter elements. You can cover all of the 80 meter band with reasonable SWR using a “cage dipole”. That is what they do at W1AW. At VHF/UHF, you may see bowtie antennas, which are also low-Q.
wunder K6WRU Walter Underwood CM87wj http://observer.wunderwood.org/ (my blog) > On Aug 4, 2016, at 3:55 PM, Guy Olinger K2AV <k2av....@gmail.com> wrote: > > Hi Fred, > > Loss *anywhere* would broaden the antenna. Famously the B&W folded dipole, > fed at the center of one wire, and terminated with an RF resistor at the > center of the other, has for decades been serving commercial installations > with widely separated operating frequencies not connected by any fortunate > harmonic relationship. That antenna has roughly an intentional 3 dB loss at > a designed position in the antenna. See > https://www.bwantennas.com/images/fdipole.gif for a drawing. > > In the case of your EFHW, the broadening loss is the dielectric loss in the > fence itself, and in the ground very close underneath. > > The B&W folded dipole as a solution sticks in the craw of a lot of hams, > because we always think there is some way to navigate the problems and keep > the 3 dB for ourselves. The thought of heating up the air with half the > power out from out two kilo-buck brick-on-key PileUpBuster brand amp just > bothers us no end. > > And where the power to the antenna cannot be increased by 3 dB to > compensate, if we regularly work the barely open paths on the low bands for > new DX and contest multipliers, that 3 dB can make a huge difference. > > BUT... > > If we are just dodging the HOA, vs creating a remote site, or not operating > at all, what you describe seems quite reasonable. One half wave on 80, two > on 40, three on 30m, four on 20m, etc. allow a rather simple feed > mechanism, and any sloppiness will be mitigated to some degree in the > unavoidable dielectric loss of the fence and ground. > > In the past, particularly with tetrode final tube(s), a pi network would > absorb ugly antenna impedances just by load and tune, easily servicing > impedances that would croak transistor amps. Back in 1959 I regularly > worked the traffic nets end-feeding 120 feet of wandering wire up about 20 > feet against a ground pipe, fed with about 30 feet of coax directly from an > 807 tetrode and a pi network. I was not loud, but I won a BPL medallion. A > later addition of a home brew 250TH amp improved things quite a bit for the > folks on the other end, but the antenna was as much as I could ever do from > that location. > > 73, Guy K2AV > > On Thu, Aug 4, 2016 at 6:22 PM, Fred Jensen <k6...@foothill.net> wrote: > >> Ummm ... my HP48GX says 102' is very very close to 3 half-waves at 14 MHz >> which sounds sort of resonant-ish. Maybe a little known bug in my >> calculator? >> >> On a similar path, I decided to try out the 80-10 EFHW from MyAntennas as >> an HOA Stealth antenna strung along the top of a 6' fence. It's 130' long, >> has a 6 turn series inductor wound on a Sch 40 PVC fitting a short distance >> out from a heavy-ish box with an SO-239. I figured there might be a 50 ohm >> resistor in the box a la the famous B&W folded dipole that graces many >> National Guard Armories. >> >> The impedance sweep when I got it yielded close enough to 50+j0 ohms on >> all bands ... except 60 m that my K3/100 is happy without the KAT3. It >> also revealed nearly infinite impedance between the bands, sort of ruling >> out the resistor [I've come to believe it's a transformer, maybe of the >> "auto" variety]. >> >> It works surprisingly well. On 80 and 40 it's pretty NVIS, which happens >> to be what I'm looking for. Above 40, the pattern starts to become more >> complex and much less vertical if I can believe EZNEC. 6' AGL is obviously >> not optimal ... except for our HOA and the CC&R's ... but I'm very >> surprised at how well it does, especially at the bottom of the cycle. >> >> This list seems to have a number of antenna experts aboard [and maybe a >> few who play antenna experts on TV] ... would anyone like to 'splain to me >> how it achieves low SWR on all bands? I could probably ferret that out >> with enough time, but if someone already knows ... >> >> 73, >> >> Fred K6DGW >> Sparks NV >> Washoe County DM09dn >> >> On 8/4/2016 1:41 PM, Wes Stewart wrote: >> >> It's a pity that too many newcomers, as well as many oldsters, are >>> enamored by this piece of wire. First, a 102' length is not resonant on >>> 20-meters, so in common jargon, it's *n >>> >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:Elecraft@mailman.qth.net >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html >> Message delivered to k2av....@gmail.com >> > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to wun...@wunderwood.org ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
